In the telephone network today, many collect calls go uncompleted. The reason for this often is that the call is unacknowledged by the called party, i.e., the called party is busy or does not answer. Thus, there is a loss of revenue to the telephone companies which cannot charge for these uncompleted calls.
It is known that an unacknowledged non-collect call can be routed to a messaging system that serves the called party. If a call is so routed, the caller pays for the time that he speaks to the messaging system as if the call was completed to the called party.